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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Protection against interference of starting currents of electric motors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors When household electrical appliances are connected to the network, impulse noise is sometimes visible on the screen of TVs and computer monitors, which reduces the quality and stability of the image. Impulse interference that occurs at the moment of closing the contacts of starting relays or switches of electric motors, with an amplitude of several thousand volts, with a fivefold starting current lasting several milliseconds, freely penetrates into the power supply circuits of electronic equipment, putting them out of action. The input filters of consumer radio electronics cannot always protect the electronic components of radio equipment. Special suppressors are commercially available that are equipped with a surge protection circuit, but they do not always successfully protect consumer electronics from the penetration of impulse noise and overvoltages. It is desirable to create an obstacle for the output of surge voltages from household electrical appliances equipped with powerful electric motors. With a reduced, at the time of starting the electric motor, mains voltage, the starting load current will decrease to the operating state, which will prevent the occurrence of radio interference and overvoltages in the mains. You can reduce the starting current in several ways: reduce the load power, reduce the voltage at the contacts of the starting relay at the moment of opening, or perform the initial acceleration of the motor speed with a current less than the starting one, transfer it from static to dynamic mode - the level of interference will be insignificant. A variant of an electronic device for reducing impulse noise is made in Fig.1.
The electronic circuit has a negative feedback circuit to stabilize the output voltage. Product Features:
scheme The circuit consists of input and output network filters, consisting of LC circuits, a surge suppressor on the HL2 LED, a programmable motor start timer DA1 and a key current regulator on the thyristor VS1. The device operates in automatic mode. The timer turns on only at the moment when the load appears on the outputs ХЗ, Х4. The mains voltage drop across the VD1 diode bridge will turn on the T1 transformer, the secondary voltage rectified by the VD2 diode bridge will go through the limiting resistor R 4 to power the timer DA1. The VD3 zener diode maintains a voltage of 13 V. To smooth out the ripple of the rectified voltage, a capacitor C5 is installed, the HL1 LED indicates the presence of a supply voltage. The optocoupler U1 circuits are powered by unstabilized voltage directly from the VD2 diode bridge. The operation of the entire device is controlled by a programmable timer on a DA1 chip of the NE555P type, its purpose is: generating rectangular pulses to control a key device on a VS1 thyristor, turning on the device with a time delay from the start of closing the contacts of the starting load relay and supplying voltage exponentially with an increase to the nominal value, voltage stabilization on load. Resistor R15 sets, if necessary, the duty cycle of the pulse, and R12 - the turn-on delay time. The rectangular pulse generator, created on the DA1 timer, produces rectangular pulses with a variable duty cycle depending on the ratings of the RC circuit: R14, R15, C8. Capacitor C7, connected to pin 4 DA1 - resetting the timer, allows after 5 ... 30 ms to raise the voltage at the load, through the key transistor, exponentially, to the nominal value, controlling through the thyristor optocoupler U1, the firing angle of the power thyristor VS1. A smooth increase in voltage from zero to the maximum value eliminates the possibility of creating an electric arc load on the contacts of the starting relay with subsequent radio interference and overvoltage in the mains. At the same time, the voltage at output 3 DA1 is reset to zero, regardless of the status of other outputs. An increase in the voltage of the error created by increasing the input mains voltage on the secondary winding of the transformer T1 leads to the opening of the transistor VT2 - feedback, the voltage at pin 5 of DA1 - modification of the timer circuit decreases, which will affect the duty cycle. The pulse frequency at output 3 DA1 will increase due to a decrease in the pause time in the pulse voltage cycle of the generator. The voltage at the load will decrease slightly, which compensates for the increase in the input mains voltage. Mains voltage dips with a duration of less than 5 ms will not affect the operation of the stabilization circuits. To create an initial voltage in the load circuits, the transistor VT1, a key voltage regulator, opens the thyristor VS1 not from the zero level, but from a higher value determined by the resistance value of the resistor R9 - the base voltage bias. A line filter is installed in the power supply circuit of the load, consisting of inductances L1, L2 and capacitors C1, C2, C3, C6 to limit the conversion impulse noise from penetration into the network, their partial damping and removal of surge voltages. The load filter is a T2 transformer with anti-parallel windings and a capacitor Sat. Fuses FU1, FU2 protect the power line from accidental short circuits in the load. Capacitor C4 eliminates interference from switching diodes of the VD1 bridge. Resistor R1 of the parallel circuit of the network diode bridge VD1 facilitates switching of the thyristor VS1 under load. Surge overvoltage limitation occurs when the impulse noise is discharged through the HL2 bipolar LED to the resistor R16. Laboratory studies have shown that surge voltages of 1500...2000 V, lasting a few milliseconds, are reduced by a factor of 30...40 when using such protection. Details Minor changes in the ratings of the elements do not affect the operation of the device. It is desirable to install the thyristor on a radiator measuring 50 * 50 mm. Power transformer T1 can be used from a network adapter with a power of up to 15 W, with a secondary voltage of 13 ... 15V. The network filter is made according to the recommendation in [1]. Coils L1,12 with 6 turns of wire with a diameter of 0,8 mm, T2 - with 10 turns of the same wire on a coil with a diameter of 10 mm, two-winding transformers from line filters of power supplies for monitors and computers are suitable. The analogue of the integral timer is the KR1006VI1 microcircuit. Resistors type MLT-0,12, R1 -2 W. Electrolytic capacitors K50-35 or TAICON", the rest - KM. Filter capacitors C4, C6 - high-voltage type K73-2 or K73-17 for a voltage of at least 600 V. places in the case can be installed and KU202N with a budget radiator.Transformer T1 type TP106-202, TP1-112 with an output voltage of 7 V at a current of 121 mA. Adjustment When checking the device, instead of a load, you can connect a 220 V 100 W electric lamp, turn on the unit in the mains and measure the voltage at the terminals X3 and X4, it should not be lower than the mains by more than 5 V, otherwise replace the thyristor or change the duty cycle of the pulse with a trimming resistor R15 . Tests of the protective device during the operation of household electrical appliances showed that the start-up time of the electric motors increased slightly by a fraction of a second, but this did not affect the operating mode. Interference from the TV screen and computer monitor has completely disappeared, the mains voltage drop from powerful inrush currents has decreased. The circuit of the protection device is mounted in a plastic case of the BP-1 type. LEDs and a load socket are installed on the top cover, the circuit diagram is assembled on a printed circuit board, some of the radio components are installed by surface mounting. Literature
Authors: V.Konovalov, A.Vanteev, Irkutsk-43, PO Box 380
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